1. Field of the Invention
The invention is related to packaging and in particular to electronic, electrical, and optical packaging.
2. Background Information
There are several levels of packaging that designers of high-speed optical communication systems must consider. One is at the chip (or integrated circuit), device, or component level, where the individual components have to be connected to printed circuit boards, for example. Discrete components have tiny wires or leads that have to be connected to printed circuit board solder pads that are usually much larger than the component""s leads. Designers must consider that the pitch of the component wires is different than the pitch of the solder pads. Designers also must consider that the length of the wires, or the distance between the component and the printed circuit board, can affect operation of the circuitry.
A third level of packaging that designers must consider is at the printed circuit board (or PCB) level. Printed circuit boards typically use epoxy glass (or FR-4) organic material as a dielectric, which limit high-speed communication capabilities because the epoxy glass absorbs some of the electrical signal, causing the electrical signal to be degraded by loss and dispersion. There may also be xe2x80x9cimpedance discontinuitiesxe2x80x9d among regions on the PCB, which produce xe2x80x9creflectionsxe2x80x9d that cause noise, ringing, etc., at high frequencies. The noise can intermingle with the signal being transmitted such that the signal becomes distorted, especially when using low signal voltages whose noise tolerance is low. All these effects create a limitation in the maximum frequency that can be propagated electrically.
Optical signal propagation has advantages for signal propagation in that it does not have the same reflection issues, electromagnetic interference (EMI) issues, or cross-talk issues as electrical signal propagation does. Optical signal propagation also tolerates a much larger bandwidth than electrical signal propagation.